Electrochemical capacitor

ABSTRACT

An electrochemical capacitor includes an ionically conductive polymer thin film, a liquid electrolyte absorbed in the polymer thin film, and thin flexible active electrode layers constituting anode and cathode composed of energy dense material of high intrinsic surface area positioned at either side of the electrolyte-retaining polymer thin film to tightly sandwich it between the electrode layers. In one embodiment, the capacitor includes a polymer electrolyte in which a polymer thin film is cast from the base polymer and impregnated with the electrolyte solution, which contains a salt for ionic conduction. In another embodiment, the base polymer material includes an ionically conducting polymer, a perfluorocarbon polymer backbone to which sulfonic acid sites are permanently anchored. The energy dense material of the electrode layers may be physically mixed with battery active material to enhance the capacity and discharge time of the capacitor. In fabrication, the electrode material is reduced to particle size suitable for application to a thin film metallized polymer substrate, and applied directly and adherently on opposite sides of the substrate by injection, spraying, or evaporation, and a final thin flexible film of each electrode is formed with a desired thickness by use of rods if a slurry, or by controlling the extent of spray or evaporation, followed by curing. In another embodiment, the electrode elements are laminated directly onto opposite sides of a single- or double-metallized polymer substrate.

BACKGROUND OF THE INVENTION

The present invention relates generally to electrochemical double-layercapacitors, and more particularly to structure and method of manufactureof such capacitors utilizing polymer electrolytes with increased energyand power densities, improved stability, lower leakage, lowermanufacturing cost and improved form factor.

Increase in volumetric energy density, high cycle life, greaterreliability and low cost are some of the most important requirement forcapacitors utilized in various military and commercial applications.Conventional dielectric capacitors such as plastic film capacitors andceramic capacitors can accumulate and deliver electric charge veryrapidly, i.e. they can operate in pulse mode with pulse widths in thenanosecond (ns) scale. However, their charge storage capability israther poor compared to electrochemical capacitors. A dielectriccapacitor with planar metal plates has capacitance in the range of picoto nano farads (pF, nF, resp.) per square centimeter (cm²) (B. E.Conway, Journal of the Electrochemical Society, Volume 138, p. 1539,(1991); I. D. Raistrick, Electrochemical Capacitors, LA-UR-90-39(January 1990); B. E. Conway, “Electrochemical Supercapacitors:Scientific Fundamentals and Technological Applications” KluwerAcademic/Plenum Publishers (1999).

Plastic film capacitors can be tailored for very high voltages simply byadjusting the film or dielectric thickness in the capacitor. The energydensity of commercial film capacitors based on polyester orpolypropylene is less than 1 joule per cubic centimeter (J/cc).Impregnated film capacitors have a very narrow operating temperaturerange while the metallized version can operate up to 100° C. with theexception of polyphenylene sulfide and Teflon™ that can reach anoperating temperature range of 200° C.

Ceramic capacitors have an attractive form factor, highcapacitance-voltage (CV) density, very good thermal withstanding, andhave been widely used as miniature devices in low stress applications.Unfortunately, in power applications that require large capacitance,high voltage and excellent volumetric efficiencies, ceramic capacitorshave not met expectations.

Electrolytic capacitors, as exemplified by the aluminum and tantalumelectrolytics, also suffer from a number of performance limitations. Thedielectric constants of the aluminum oxide and tantalum oxidedielectrics are about 10 and 28, respectively. Their breakdown voltagesare at least an order of magnitude lower than polymers, however,offering little if any net advantage. Their maximum operating voltage isabout 400 volts (V). Highest practical energy density achieved has beenabout 3 J/cc. They suffer from relatively very high leakage, very highdissipation factor (DF), hydrogen and electrolyte outgassing, reformingperiodically, high equivalent series resistance (ESR) and form factor.At frequencies above 200 kilohertz (KHz), electrolytic capacitors failfrom dielectric instability and poor impedance response.

Electrochemical capacitors are symmetric devices in which theelectrolyte is placed between two identical electrode systems. Whileelectrochemical capacitors can store and deliver charge in the timescale of the order of several tens of seconds, their ability to delivercharge at short times is dictated by kinetics of the surface redox(oxidation-reduction) reactions and combined resistivity of the matrixand electrolyte. Electrochemical capacitors fall into two broadcategories: (1) double layer capacitors which rely solely on interfacialcharge separation across the electrical double layer; and (2)pseudocapacitors which have enhanced charge storage (similar to abattery, but to a lesser extent) derived from faradaic charge transferin parallel with the double layer. The double layer, created naturallyat an electrode/electrolyte interface, has a thickness of about 10Angstroms (A). For a high area electrode, the capacitance per unitgeometric area is amplified by the roughness factor, which couldapproach 100,000 times. The specific capacitance is further increased inelectrode systems having a substantial potential region over which afaradaic reaction (similar to a battery reaction, but to a lesserdegree) takes place. Thus electrochemical capacitors, unlike theirelectrostatic counterparts, can accumulate substantial charge, becauseof the molecular level charge separation coupled with the high chargedensity associated with the surface redox processes on high areaelectrodes.

The projected energy density for electrochemical capacitors is twoorders of magnitude lower than that of batteries, but power densitiesare several orders of magnitude higher. Energy density is much betterthan for conventional film capacitors but in terms of power, theelectrochemical capacitors are more suitable for relatively longdischarges (milliseconds (ms) to several seconds) and low tointermediate power applications. Carbon capacitors exhibit high cyclelife and good stability, thus making them useful in applications such aslightweight electronic fuses, backup power sources for calculators, andsurge-power delivery devices for electric vehicles. Recently, carboncapacitors have been used in small toy cars. Carbon based capacitorsutilize very thick electrodes in their construction, resulting in poorparticle to particle contact of the agglomerate and high ionicresistance from the electrolyte distributed in the microporousstructure. The electrodes are made highly porous allowing for air andsulfuric acid to penetrate deep into the porous structure to achieve thefull benefit of the surface area. Although this results in highcapacitance and energy density, the ESR increases as a result of thehighly porous and thick structure.

Although the pseudocapacitors utilizing valve metal oxide electrodessuch as ruthenium or iridium oxide possess very high double layercapacities emanating from the intrinsic high surface areas and redoxprocesses, leading to energy densities as high as 10 to 20 J/cc, theysuffer from the same limitations as the carbon capacitors with high ESR.Ruthenium oxide has a high double layer capacity of about 150microfarads per real square centimeter (μF/real cm²). Since theintrinsic surface area of this material is very high, it is probablethat the intrinsic capacitance will also be extremely high. Thesuperior, demonstrated performance of the RuO₂-based capacitor is aconsequence of the high exchange current density of the RuO₂/Ru₂O₃reaction, although this advantage is negated by the porous nature of theRuO₂ matrix used in such devices. Craig, in Canadian Patent No.1,196,683 (1985), describes a supercapacitor based on ruthenium oxideand mixtures of ruthenium and tantalum oxides and reported capacitancesas high as 2.8 F/cm². Increase in the ESR of the capacitor is aconsequence of the reduction in the exchange current density. This maybe overcome if the capacitor is designed with ultra-thin electrodes andhighly conductive thin film electrolytes.

Electrochemical capacitors based on RuO₂ and solid polymer electrolytehave been studied at Giner, Inc (MA). The use of a solid polymerelectrolyte leads to a leak-free system that contains no corrosiveliquid electrolyte. This concept was based on the use of a hydratedionomer membrane such as DuPont's Nafion™. The composite structureensured a continuous proton-conducting ionomer linkage throughout asingle cell, thus facilitating proton transport from one electrode tothe other. The performance of this capacitor containing only hydratedwater dropped off abruptly below the freezing point of water and inaddition, the ESR was fairly high at about 0.3 ohm-cm². Subsequent useof sulfuric acid improved the proton conductivity within the particulateby accessing pores down to 100 A diameter.

This study was interesting and demonstrated that high protonconductivity and materials based on very high exchange current densitiesis effectively required for lowering the ESR. However, the problem withusing Nafion™ type membranes is that they are fairly thick, resulting inhigh internal resistance and also very weak polymers. Swelling of themembrane by the sulfuric acid decreases its strength and conductivityeven further. A polymer electrolyte that can be mechanically stable anddesigned in very thin film and highly conducting form would be desirablefor reducing the internal resistance.

In order to obtain high energy content per unit weight and volume, it isnecessary to utilize electrochemically active materials of significantlyhigher energy content than in present commercial capacitors. The bestpossibilities lie in a capacitor that incorporate materials based onhigh surface area activated carbon or valve metal oxides such as RuO₂.Furthermore, in order to access the entire porous structure of RuO₂efficiently and achieve high capacitance (hence, high energy) and highpower at low ESR, the electrode needs to be designed in very thin filmform. Thinner electrodes are more feasible with pseudocapacitors thanwith double layer capacitors due to the greater capacitance density ofthe former.

Experience has shown that higher cyclability, higher power, lowerinternal resistance and greater capacity utilization is favored bydesigns that incorporate very thin electrode and electrolyte structures.Ultra-thin electrode and electrolyte will overcome kinetic constraintson the specific power, cycling efficiency and capacity utilization. Thethinner the electrode, the shorter is the time needed to access regionsof the structure farthest from the macroscopic electrode/electrolyteinterface, thus opening up the possibility of constructing the morecompact bipolar stacks necessary for high voltage, pulse powerapplications. In addition, improving the capacity of the electrode is avery important feature for devices that requires very long dischargetimes such as, for example, in electric vehicles or in cellulartelephones.

The energy density of an electrochemical capacitor can further beincreased if very thin inactive substrate materials such as metallizedplastic current collectors are used. The use of such substrates willalso result in low-cost devices. Electrochemical capacitors are lowervoltage devices; aqueous based are 1 V/cell and non-aqueous based areabout 3 to 4 V/cell. Connection of devices in series to obtain highervoltages results in a decrease in capacitance as well as an increase inESR, according to the number of units in series. One of the advantagesof using liquid organic electrolytes is the theoretical widerelectrochemical window. An immediate consequence is an increase of theenergy density (Energy=½(CV²), where C is static capacitance) and thepower (Power=V²/R) densities.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toprovide a base polymer material for a polymer electrolyte that isdimensionally stable in the liquid solvents, aqueous or non-aqueous,presently used in electrochemical capacitors, and that is highly stablewith temperature.

Another object of the invention is to provide a base polymer materialfor a polymer electrolyte that exhibits little or no swellingcharacteristics when in contact with liquid solvents, compared to priorart membranes.

Another object of the invention is to provide a base polymer materialthat is predominantly amorphous in nature.

Still another object is to provide a base polymer material for a polymerelectrolyte that is mechanically stronger than prior art membranes whenin contact with liquid solvents.

Still another object is to provide a polymer electrolyte with high ionicconductivity.

Yet another object of the invention is to provide polymer electrolytecompositions which are more conductive at lower levels of liquidsolvents than prior art polymer electrolyte-solvent compositions.

Another object of the invention is to provide polymer electrolytecompositions in ultrathin film form.

Another object of the invention is to provide polymer electrolytecompositions with a wide temperature range of operation.

Yet another object of the invention is to provide polymer electrolytecompositions with ionomer or ionically conductive backbone to furtherfacilitate the conduction process.

A further object of the invention is to provide polymer electrolytecompositions in which the solvent is immobilized in the polymer, toallow electrochemical capacitors constructed from such compositions tobe used in any orientation.

Another object of the invention is to provide polymer electrolytecompositions that can be manufactured in very thin film form, providelow resistance and excellent flexibility.

Yet another object of the invention is to provide electrochemicalcapacitor electrodes that are ultra-thin and conductive.

Still another object of the invention is to provide methods ofmanufacturing such ultra-thin and conductive electrodes.

Another object of the invention is to provide electrochemical capacitorelectrodes with high capacity.

Still another important object of the invention is to provide anelectrochemical capacitor with polymer electrolyte compositions andultra-thin electrodes described in the preceding enumerated objects.

A further object is to provide such electrochemical capacitors withultra-thin current collectors such as very thin metallic elements ormetallized polymer substrates for improved energy density, powerdensity, higher capacity utilization, higher cycle life, greatercharge-discharge efficiencies, lower ESR, greater safety, and greaterreliability, and which can be produced at high speed, lower cost, andwith improved form factors.

Another object of the invention is to coat the thin substrate with verythin active anode and cathode material.

A related object is to laminate the anode and cathode elements on bothsides of the metallized polymer substrate material so as to yield ahighly flexible electrode.

The electrolyte of the present invention is preferably a protonconductor or is very conductive, is very flexible and somewhat dry, isof low cost, and in some preferred embodiments of the invention isconstructed in very thin film format. Polymer electrolytes of thisdesign can be combined with various similar electrode materials such ascarbon, materials from the valve metal oxides to provide electrochemicalcapacitors having high specific energy (Wh/kg) (gravimetric) and energydensity (Wh/l) (volumetric), high cycle life, low ESR, low leakage, andwhich provide improved safety.

One embodiment of a solid base polymer material of a polymer electrolyteof an electrochemical capacitor according to the invention is a thinfilm polymer selected from a group consisting of polyester (PET),polypropylene (PP), polyethylene napthalate (PEN), polycarbonate (PC),polyphenylene sulfide (PPS), polyvinylidene-fluoride (PVDF), andpolytetrafluoroethylene (PTFE), or a combination of two or more thereof.The specific polymer and its concentration in the polymer electrolyteare selected to tailor at least one desired property of the polymerelectrolyte. The base polymer material may include aperfluorocarbon-sulfonated ionomer electrolyte such as Nafion™,2-acrylamido-2-methyl propane sulfonate (or AMPS), or the Dow membraneXUS13204.10 or other ionomer materials based on different blends offluoropolymers, including poly(chlorotrifluoro-ethylene),poly(ethylene-chlorotrifluoroethylene), poly(fluorinatedethylene-propylene), polytetrafluoroethylene, hexafluoropropene andpolyvinylidene-fluoride (PVDF) and mixtures of these ionomers. Suchmaterials have a perfluorocarbon polymer backbone to which sulfonic acidsites are permanently anchored. Or the base polymer material may includean ionically conducting polymer such as an acrylate, polyethylene oxide(PEO), polypropylene oxide (PPO),poly(bis(methoxy-ethoxy-ethoxide))-phosphazene (MEEP), polyacrylonitrile(PAN), polymethylmethacrylate (PMMA), polymethyl-acrylonitrile (PMAN),or other suitable ionically conductive polymer or a combination ofionically conductive polymers, and so forth.

In another embodiment, an electrolyte-retaining base polymer materialfor an electrochemical capacitor is a polymer thin film cast from asolution of the base polymer such as PVDF and acrylate monomer/oligomerradiation cured after which a solvent in which those constituents weredissolved has substantially evaporated. A liquid or semi-liquidelectrolyte solution containing a salt for ionic conduction such as aquaternary phosphonium (R₄P⁺) salt, or a quarternary ammonium salt(R₄N⁺), or a metal salt such as sodium, lithium, potassium, magnesium,or calcium salt, more preferably lithium, is absorbed within the thinfilm. R in this case is an alkyl group while the anion of the salt maybe chosen from hexafluorophosphate (PF₆ ⁻), perchlorate (ClO₄ ⁻),tetrafluoroborate (BF₄ ⁻), hexafluoroarsenate (AsF₆ ⁻),tetrachloroaluminate (AlCl₄ ⁻), trifluoromethanesulfonate (CF₃SO₃ ⁻),methide (C(SO₂CF₃)₃ ⁻ and bis(trifluoromethane sulfonyl) imide(N(CF₃SO₂)₂ ⁻). In certain embodiments, the salt is a plasticizer saltsuch as lithium imide or methide.

The liquid electrolyte may be chosen from a wide variety of solvents,including aqueous based sulfuric acid, or a non-aqueous based chosenfrom ethylene carbonate, propylene carbonate, dimethoxy methane,dimethoxy ethane, tetrahydrofuran, dimethoxy carbonate, diethylcarbonate, acetonitrile, or mixtures of such liquids or any othersuitable organic solvents.

In a process of manufacture of this embodiment, the PVDF and acrylatemonomer/oligomer are dissolved in a hydrocarbon solvent such as N-MethylPyrrolidone (NMP) to form a polymer solution, which is then cast in athin film, in part by evaporation of the solvent. The film is thensoaked in an appropriate liquid electrolyte solution containing anappropriate salt, for absorption of the electrolyte within the film, andthe acrylate monomer/oligomer is cured by subjection to electron beam orultraviolet radiation.

A dimensionally stable, highly resilient embodiment of a polymersolid-solution blend film for an electrochemical capacitor, the filmbeing capable of electrolyte retention without appreciable swelling, isproduced by a method in which PVDF and AMPS are mixed homogeneously toform a polymer blend thereof. A very high surface area inorganicfiller—either fumed silica or alumina—having an average particlesize<0.05 micron (μum) in diameter and a surface area of at least about100 m²/g is then dispersed with a concentration in a range from about0.1% to about 30% by weight into the copolymer blend to enhance theporosity and mechanical stability of the thin film into which thecopolymer blend with inorganic filler is cast. Finally, the resultantfilm is soaked in a liquid solvent electrolyte for absorption andretention in the film. Preferably, the film is soaked in an aqueousbased solvent such as sulfuric acid or a liquid organic electrolytesolvent, each of the solvent containing a salt for ionic conduction. Theliquid electrolyte is immobilized in the AMPS/PVDF polymer to allowmolecules of the liquid polymer (AMPS) to trap molecules of theelectrolyte into pores of the film. Preferably, the liquid polymer iscross-linkable based on AMPS, or other suitable materials such asacrylates and PEO-based materials, and radiation curing is performed tocross-link the liquid polymer for trapping of molecules. Alternatively,some immobilization of the liquid organic solvent electrolyte may beachieved by using a non-ionizable liquid polymer. Dispersion of theinorganic filler into the polymer blend is performed during blending ofthe PVDF and AMPS.

Also provided by the present invention is an anode and cathodeconsisting of a first group material(s) possessing properties of highexchange current density, intrinsically high surface area, and highcharge capacity in combination with a second group material(s) thatessentially has an exceptionally high redox capacity. The first group ofmaterials comprise activated carbon or valve metal oxides. Suchmaterials consist of oxides of titanium, zirconium, hafnium, niobium,tantalum, molybdenum, tungsten, ruthenium, iridium, platinum, palladium,osmium, gold, and rhenium. The second group of materials are selectedfrom a wide range of oxides, sulfides and selenides, or any other groupwell known in the prior art that are used in lithium batteries, e.g.MnO₂, LiMn₂O₄, Li_(x)MnO₂, MoS₂, MoS₃, MoV₂O₈, CoO₂, Li_(x)CoO₂, V₆O₁₃,V₂O₅, V₃O₈, VO₂, V₂S₅, TiS₂, NbSe₃, Cr₂O₅, Cr₃O₈, WO₃, Li_(x)NiO₂,Li_(x)Ni_(y)Co_(z)O₂, Li_(x)Ni_(y)Mn_(z)O₂, Li_(x)Co_(y)Mn_(z)O₂,lithium doped electronically conducting polymers such as polypyrrole,polyaniline, polyacetylene, and so forth. The first group of materialsmay be single oxides or multiple oxides. The second group of materialsmay consist of one compound or a mixture of compounds. The compositionof the first group materials is 1 to 99% while the balance is from thesecond group of materials.

A method of producing an embodiment of the invention includes physicallymixing the activated carbon or valve metal oxide or oxides with thebattery active material to enhance the discharge time of the capacitor.

A method of producing another embodiment of the invention includesblending electrode active materials with polymer electrolytes of theabove compositions.

A method of producing yet another embodiment of the invention is tofabricate ultra-thin thin film electrodes of these material in athickness in a range from 1 μm to more than 100 μm.

Any of these polymer electrolyte films and electrodes may be used toform an electrochemical cell, particularly an electrochemical capacitor,by tightly sandwiching the film between thin, flexible active anode andactive cathode layers.

For example, one embodiment of a thin film electrochemical capacitor isformed from a resilient flexible polymeric electrolyte thin film thatincludes a base polymer with inorganic filler dispersed therein toincrease surface area and porosity of the film, impregnated with asemi-liquid or even dry solution of liquid polymer, organic solventelectrolyte and a salt; and a pair of spaced-apart flexible thin filmelectrodes, each including a polymer substrate having an adherentelectrically conductive layer of the above mentioned metallic materialthereon, the polymer electrolyte film being tightly sandwiched betweenthe pair of thin film electrodes. The polymer substrate of each of theanode and cathode is preferably selected from a group of polymersincluding PET, PP, PPS, PEN, PVDF and PE, and each polymer substrate ismetallized to form the conductive layer thereon. The ultra thin filmmetallized polymer substrate has a thickness in a range from about 0.5micron to about 50 microns, thereby rendering it very flexible for easeof coating and handling, to avoid kinking and deformation thereof,during manufacture of electrochemical capacitors.

The electrochemical capacitor polymer substrate may comprise a layer ofpolymer material, and a low resistance metallization layer having aconductivity in a range from about 0.01 ohm per square to about 1 ohmper square overlying and adhered to a side of the polymer material.Preferably, the layer of polymer material has a non-metallized marginwith a width in the range from about one mm to about three mm.Preferably, also, a low resistance metallization layer having aconductivity in the aforementioned range overlies and is adhered to eachside of the polymer material, and both sides of the layer of polymermaterial have such a non-metallized margin present at the same edge ofthe layer of polymer material.

According to another aspect of the invention, an electrochemicalcapacitor electrode comprises an ultra thin film metal substrate for atleast one of a cathode substrate and an anode substrate of anelectrochemical capacitor, the ultra thin film metal substrate having athickness in a range from about one micron to about 10 microns and maycomprise one of the following metallic materials chosen from aluminum,copper, nickel, titanium, stainless steel, or an alloy such as inconelor any other suitable stable metallic material.

According to another aspect of the invention, the selected metal oralloy is etched either physically or chemically to increase thesubstrate intrinsic surface area.

According to yet another aspect of the invention, a method offabricating a thin film electrochemical capacitor includes incorporatingan ultra thin film metallized polymer substrate in the capacitor duringfabrication thereof, wherein the polymer layer in the substrate has athickness in a range from about 0.5 micron to about 50 microns, inconjunction with very thin film capacitor electrode/electrolytestructures having thickness less than 5 microns, respectively, whereinthe thickness of the metallization layer on the polymer layer isselected according to desired conductivity thereof

The invention also provides novel methods of coating an ultra thin filmmetallized polymer substrate for a thin film electrochemical capacitorwith very thin film active anode material and active cathode material.One method comprises steps of milling each of the anode material and thecathode material in a separate solvent to reduce the particle size ofthe respective material, injecting respective ones of the materialsdirectly onto the substrate at opposite sides thereof, and subsequentlydrawing each of the materials at opposite sides of the substrate into athin film of desired thickness using wire wound rods or Mayer rods ofdifferent wire diameters to control wet slurry thickness. The substrateis coated on one side of the metallized polymer substrate, rather thanboth sides. Coating an anode on one side and a cathode on the other sidewould only apply to a bipolar electrode.

Another coating method includes incorporating each of the materials intoits own aerosol mix, spraying atomized aerosol of each material directlyon respective opposite sides of the film substrate while moving saidsubstrate past the points of aerosol spray at high speed, and curing thesprayed material either by drying or radiation. Yet another coatingmethod comprises evaporating the respective electrode material directlyonto respective opposite sides of the substrate.

Also according to the invention, a method of fabricating a thin filmelectrochemical capacitor involves laminating anode and cathode elementson respective opposite sides of a double-metallized polymer substrate,whereby to yield a highly flexible electrode structure for thecapacitor. Non-metallized margins are provided on each of the anode andcathode elements on the opposite sides of the metallized polymersubstrate, and metal is sprayed on opposite ends of the laminatedmetallized polymer substrate for terminations thereto. These techniquesenable the provision of a ratio of substrate thickness to activeelectrode thickness less than about 0.5.

Also according to the invention, a method of fabricating a thin filmbipolar element is provided involving laminating anode and cathodeactive elements on respective opposite sides of a double-metallized ofthe same polymer substrate which has been impregnated with anelectronically conductive material within the polymer substrate such ascarbon black or metallic elements (inert to the active electrode),whereby to yield a highly flexible and strong electrode structure forthe capacitor.

Also according to the invention, a method of fabricating a thin filmbipolar element is provided as described immediately above, but thedouble-metallized and conductive polymer substrate is replaced by a verythin film metallic substrate.

Also, according to the invention is provided, a method of forming abipolar element is provided also as described above, but with a coatingof polymer electrolyte on each side of the bipolar electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and still further aims, objectives, features, aspects andattendant advantages of the present invention will become apparent fromthe following detailed description of certain preferred embodiments andmethods of fabrication of a thin film electrochemical capacitor inaccordance with the invention, constituting the best mode presentlycontemplated of practicing the invention, when taken in conjunction withthe accompanying drawings, in which:

FIGS. 1A, 1B and 1C are sectional side views of different polymersubstrate electrode structures for a thin film electrochemicalcapacitor, in which FIG. 1A illustrates a structure of a metallizedplain polymer film with an unmetallized margin having a coating ofactive cathode material not on the margin; FIG. 1B illustrates astructure of a metallized plain polymer film with an unmetallizedmargin, but having layers of active anode material and polymerelectrolyte not on the margin; and FIG. 1C illustrates a dual electrodestructure in which an electrode element is laminated on respectiveopposite sides of a double-metallized polymer substrate;

FIG. 2 is a sectional side view of a composite electrochemicalcapacitor;

FIG. 3 is an exploded sectional side view of a capacitor structure inwhich a polymer substrate of an electrode is impregnated with anelectronically conductive element inert to the active electrode andmetallized on both sides of the substrate without a margin; and

FIG. 4 is a perspective view of a wound electrochemical capacitor,illustrating its principal webs including an anode, a hybrid polymerelectrolyte film, and a cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND METHODS

According to a first aspect of the present invention, a range of basepolymer compositions is provided for the membrane of the electrochemicalcell with improved chemical stability in liquid solvent electrolytes andimproved chemical stability as a function of temperature. Polymermaterials with high breakdown voltages or strengths and low dissipationfactors, such as those employed in film capacitors, have been found tobe chemically more stable than other materials with liquid organic oraqueous solvents.

A preferred base polymer material for making a room temperature highlyconductive polymer electrolyte contains one selected from a group havingpronounced ionic conductivity, and the other selected from a secondgroup consisting of polymers which are non-ionically conductive. Thesecond polymer serves to provide the basic backbone or strength of thefinal polymer electrolyte when manufactured in ultra-thin films.However, if the polymer material selected from the first group providessufficient strength to the polymer electrolyte, a polymer from thesecond group need not be included in the composition of the base polymermaterial. Likewise, if a polymer selected from the second group, inaddition to meeting the requisite film strength requirement alsoprovides the desired ionic conductivity to the polymer electrolyte, adifferent polymer from the first group need not be included in the basepolymer.

The first group of polymers for a base polymer material are tonicallyconductive polymers mixed with a metal salt, preferably a lithium or aquarternary alkyl ammonium or quarternary alkyl phosphonium salt.Preferably the ionically conductive polymer has a hetero atom with alone pair of electrons available for the metal ions of the metal salt toattach to and move between during conduction in the final composite, oris an ionomer containing perfluorocarbon backbone with sulfonatedchains. It is preferred that the polymer is chosen from a wide range ofsolid polymeric materials, including those based on linear polymers sucha poly(ethylene oxide) or PEO; random copolymers such as oxymethylenelinked PEO; block copolymers such as PEO-PPO-PEO crosslinked withtrifunctional urethane; comb-branched block copolymers such aspoly(bis(methoxy-ethoxy-ethoxide))-phosphazene or MEEP; networkstructures such as triol-type PEO crosslinked with difunctionalurethane; single ion conductors such aspoly((oligo)oxyethylene)methacrylate-co-alkali metal methacrylate,polyacrylonitrile (PAN), polymethylmethacrylate (PMA);polymethylacrylonitrile (PMAN); polysiloxanes and their copolymers andderivatives; polyvinylidene fluoride or chloride and copolymers of theirderivatives; perfluorocarbon-sulfonated ionomer materials such asNafion™, 2-acrylamido-2-methyl propane sulfonate (or AMPS), or the Dowmembrane XUS13204.10 or other ionomer materials based on differentblends of fluoropolymers, including poly(chlorotrifluoro-ethylene,poly(ethylene-chlorotrifluoroethylene), poly(fluorinatedethylene-propylene), polytetrafluoroethylene, hexafluoropropene, andmixtures of the these ionomers; polymers based on a wide variety ofacrylates available in the industry; or any other polymers orcombination of the above polymers either condensed or cross-linked toform a different polymer or mixed physically, which are combinable witha metal salt, such as a lithium, ammonium or phosphonium salt, toenhance the polymer's ionic conductivity. Even a modestly conductivepolymer such as PEO works very well in the electrolyte composition ofthe present invention, and polymers such as acrylates or MEEP, whichpossess higher ionic conductivities with a lithium salt should performat least as well as PEO in the electrolyte compositions of the presentinvention.

A suitable base polymer material is complexed with a conductive saltsolution. Salts which may be combined with the base polymer materialinclude suitable salts of sodium, lithium potassium, calcium, magnesium,ammonium, phosphonium. Preferably a plasticizer salt of a metal, e.g.lithium bis(trifluoromethane sulfonyl)imide(LiN(CF₃SO₂)₂ or lithiumimide), lithium methide (LiC(SO₂CF₃)₃), lithium hexafluorophosphate(LiPF₆), lithium perchlorate (LiClO₄), lithium tetrafluoroborate(LiBF₄), lithium hexafluoroarsenate (LiAsF₆), lithiumtetrachloroaluminate (LiAlC1 ₄), and lithium trifluoromethanesulfonate(LiCF₃SO₃) is used. Another preferable salt is a quarternary alkylammonium or quarternary alkyl phosphonium salt of the above lithium saltanions.

The liquid electrolyte solution may be chosen from a wide variety ofsolvents, including aqueous based sulfuric acid, or non-aqueous basedorganic liquids chosen from among ethylene carbonate, propylenecarbonate, dimethoxy methane, dimethoxy ethane, tetrahydrofuran,dimethyl carbonate, diethyl carbonate, acetonitrile, or mixtures of suchliquids or any other suitable organic solvents.

A particular salt solution is chosen such that, when added to a polymersuch as MEEP, the base polymer/salt mixture yields a conductivity of atleast about 5×10⁻² S/cm at 25° C. On the other hand, a particular saltsolution such as one molar tetraalkyl ammonium borate in aqueoussulfuric acid when added to AMPS polymer and cured yields a conductivityof at least 1 S/cm at 25° C. Polymers based on various acrylatecompositions and lithium imide also yield good conductivity values. Aparticular liquid solvent or solvents are chosen to provide chemicalstability, excellent ionic conductivity when combined with a particularsalt, and thermal stability. Organic liquids based on 50:50 ethylenecarbonate and propylene carbonate and 1M lithium imide yieldconductivities as high as 3×10⁻² S/cm while liquids based onacetonitrile can be used at significantly lower temperatures down to−40° C.

The second group of polymers for use in a base polymer material orcomposition includes more inert and high strength materials such aspolyester (PET), polypropylene (PP), polyethylene napthlate (PEN),polyvinylidene fluoride (PVDF), polycarbonate (PC), polyphenylenesulfide (PPS) and polytetrafluoroethylene (PTFE). Other polymermaterials that possess similar characteristics to these polymers couldalso be used.

In a two-polymer blend, the concentration of one the polymers fromeither the first or second group is in the range from 1% to 99% byweight, the remainder of the blend being the other polymer. The specificpolymers chosen from these two groups, and their concentrations in theblend, are selected so as to tailor at least one desired property of thebase polymer material. In any case, the chosen polymers provide a basepolymer material with high temperature stability, up to at least 100° C.Most of the materials described above, including PVDF, acrylates, PEO,PPO, and the like, possess such thermodynamic or high temperaturestability.

In a process of manufacture of this embodiment, the PVDF and acrylatemonomer/oligomer are dissolved in a hydrocarbon solvent such as N-MethylPyrrolidone (NM) to form a polymer solution, which is then cast in athin film, in part by evaporation of the solvent. The film is thensoaked in an appropriate liquid electrolyte solution containing anappropriate salt, for absorption of the electrolyte within the film, andthe acrylate monomer/oligomer is cured by subjection to electron beam orultraviolet radiation. The addition of immobilized liquid salt solutionin an ionic conductor in very thin film polymer electrolytes allows theuse of lesser quantity of liquid solvents.

The applicant has found that by dispersing about 0.1 to 30% (by volumeof the final electrolyte composition) fumed silica or very high surfacearea alumina filler into a base polymer/salt intermediate composition,the ionic conductivity of the resulting mixture increases by aboutone-half to one order of magnitude above that of the polymer/saltcomplex alone. It was also observed that the electrolyte film isdimensionally stable when in contact with liquid solvent electrolytesand will not swell to any appreciable extent. One source for a suitablehigh surface area alumina preparation is Degussa Corporation.

Preferably, the inorganic filler is fumed silica, a high pure silica inan amorphous crystalline structure, which has a fine particle size and avery high specific surface area similar to alumina. The fine particlesize is highly preferred not only to maintain the high specific surfacearea but also to make the polymer electrolyte contain the silicahomogeneously dispersed. A desirable mean particle size is 0.05 micronor less, preferably 0.01 micron or less. The surface area is 100 m²/g ormore, preferably 200 m²/g. Examples of some suitable fine particlesilicas are: AEROSIL 380™, available from Nippon Aerosil; CAB-O-SIL™GARDE EH-5™ from Cabot Corporation; and SNOWTEX-O™ (a dispersion ofsilica in water or alcohol) available from Nissan Chemical IndustriesLtd. The base polymer material with an appropriate salt solution andinorganic filler may be cast using a thin film coating process.Alternatively, dispersion of the inorganic filler into the polymer blendmay also be accomplished during polymer and salt dissolution into asolvent. For some uses, the preferred filler content is 0.1-30% fumedsilica or alumina having an average particle size less than or equal to0.01 micron. In the most desirable compositions, the filler enhances theionic conductivity of the polymer materials by at least one order ofmagnitude.

Another embodiment of the invention resides in forming hybrid basepolymer blends in which the film is mechanically stronger thantraditional ionomers and the final polymer electrolyte is stronger whenin contact with liquid electrolyte. Representative examples indicatethat polymers prepared with PVDF and Nafion™ or AMPS in varying ratioswith high surface area silica or alumina inorganic filler, have greatermechanical strength than Nafion™ or AMPS alone.

Cross-linking a cross-linkable liquid polymer using either ultraviolet(UV) or electron beam (EB) radiation is the most preferred method ofimmobilizing the liquid organic solvent electrolyte into the basepolymer structure, although a non-ionizable liquid polymer may alsoreduce the mobility of the solvent from the polymer. Representativeexamples of cross-linkable polymers include those polymers based onacrylates and PEO-based materials; AMPS, and those based onnon-cross-linkable polymers include MEEP, polyacrylonitrile, and soforth. Cross-linking is most preferred because the liquid polymermolecule traps the solvent molecule during radiation curing into thepores of the base polymer. The applicant herein has found that norestriction exists on the type of liquid polymer material used. However,it is preferable to use a polymer having a hetero atom with a lone pairof electrons for the cations of the salt to latch onto and move duringthe conduction process from one lone pair site to another. In the caseof ionomers, it is preferable if sulfonic groups exist in which case itwill be either protons or lithium ions which will move from one sulfonicgroup to another.

Preferable polymers include MEEP which demonstrates excellent ionicconductivities at room temperature (10⁻⁵ S/cm), or more preferablyacrylates which have excellent solvent retention properties and can becured in-situ trapping the solvents within the polymer.

The base hybrid polymer thus formed is no longer crystalline, butpredominantly amorphous in nature.

The applicant herein has further found that the use of plasticizer saltssuch as lithium imide with ionomeric polymers containing acetonitrile asthe liquid organic solvents in base polymers containing PVDF and 20%high surface area alumina yield conductivity values at least 2 orders ofmagnitude higher than those polymer electrolytes containing conventionallithium salts and allow lower temperature performance.

It will be appreciated that the present invention allows fabrication ofvery thin, low resistance, flexible films of this polymer electrolyte,without loss of mechanical integrity, conductivity, and mechanicalstrength. By virtue of introducing the above-described preferredmethods, which produce excellent mechanical strength and porosity of thebase polymer via the copolymer hybrid design and addition of highsurface area alumina or silica, reduce the swelling properties of thepolymer with liquid solvents, reduce the level of liquid solvents intothe polymer, improve the ionic conductivity of the polymer electrolyteby introducing plasticizer salts and ionically conductive polymers intothe base polymer, and immobilizing the solvents, gelled polymerelectrolytes as thin as 5-10 microns or less can be manufactured simplyby selective use of the various components of the polymer electrolyte.Such polymer electrolytes are not only thin, but truly flexible; and thethinness of the structure allows the possibility of lower resistancesthan are available from liquid electrolytes absorbed in traditionalglass-matt separators used in present electrochemical capacitors.Traditional separator materials are usually at least 25 microns thick.The design of gelled polymer electrolytes according to the presentinvention suggests that the effective resistance for thinner polymerelectrolyte sections should be at least half that observed in liquidelectrolytes alone.

According to yet another embodiment of the present invention, anelectrochemical cell is provided having improved performance, in whichthe cell has a polymer electrolyte layer fabricated as one of theabove-described embodiments, and an anode and cathode consisting ofsimilar materials (termed electrode for simplicity). Each of the anodeand the cathode is selected from a group of materials that provides avery high capacity. The composition of the electrode comprise of twogroups of materials. The first group provide intrinsically high surfacearea for large double layer capacity, rapid kinetic charge transfer ofthe ions for high rate discharge and/or redox capacity orpseudo-capacitance. The second group provide additionally larger redoxcapacity but relatively slower charge transfer.

The first group of materials comprise activated carbon or a metal oxideor a mixture of at least two metal oxides selected from the group ofmetal oxides consisting of oxides of valve metals, noble metals, alloysof valve metals, alloys of noble metals, and mixtures of valve and noblemetals. Such materials consist of oxides of titanium, zirconium,haftium, niobium, tantalum, molybdenum, tungsten, ruthenium, iridium,platinum, palladium, osmium, gold, and rhenium. Surface area enhancementof these oxides occurs by virtue of the preferred molecular fit which ispossible using mixed-sized metal oxide molecules in latticearrangements. Thus, whereas a single metal oxide produces a mono-latticewith routine gaps where molecules abut one another, a mixed metal oxidewith differently sized molecules produces a binary lattice where thegaps of the mono-lattice may have gaps between the contact points of thetwo molecules making it up. If a third differently sized metal oxide isadded, further gap-filling is possible. Such arrangements provide ameans for substantially enhancing the surface area of the underlyingelectrode.

The metal oxides of the first group consist of oxides of valve and/orplatinum group metals capable of reversible oxidation and reduction. Incertain preferred electrodes, the mixture comprises a mixture ofruthenium oxide, iridium oxide, and tantalum oxide. The composition ofthe different mixture depends upon the desired final property and canhave a wide range of variable composition.

An unexpected finding occurred in use of the electrodes of theinvention. It was found that the addition of a second group ofmaterials, primarily those based on battery active materials, and morespecifically those based on lithium battery materials, not onlyincreases the capacity of the electrode, but allows the electrode todischarge over a prolong period of time. The active second groupmaterial is selected from the group consisting of MnO₂, LiMn₂O₄,Li_(x)MnO₂, MoS₂, MoS₃, MoV₂O₈, CoO₂, Li_(x)CoO₂, V₆O₁₃, V₂O₅, V₃O₈,VO₂, V₂S₅, TiS₂, NbSe₃, Cr₂O₅, Cr₃O₈, WO₃, Li_(x)NiO₂,Li_(x)Ni_(y)Co₂O₂, Li_(x)Ni_(y)Mn_(z)O₂, Li_(x)Co_(y)Mn_(z)O₂, ormixtures thereof. In some alternative embodiments the material mayemploy an electronically conducting polymer, which may be polypyrrole,polyaniline or polyacetylene, for example.

By way of example, the applicant has found that combiningRuO₂:IrO₂:TaO₂:MnO₂ in the ratio 1:1:1:1, enables attainment of anelectrode with at least 50% greater discharge capacity and time than ifRuO₂:IrO₂:TaO₂ is used in the ratio 1:1:1. The fast discharge timeassociated with the valve metal oxides is not compromised as a result ofadding manganese dioxide. In fact, it will be seen below that the designof electrode allows the use of the slowest kinetic battery material insuch combination. Of course, the invention is not restricted to thiscomposition or material but can be extended to a wide range ofcompositions and to different combinations of materials.

Electrochemical capacitor electrodes are traditionally made bycalendaring the electrode paste onto a nickel or stainless steel gauzeand compacting between heated rollers. The substrate material istypically about 2 to 3 mils thick while the active electrodes aretypically about 5 to 10 mils thick, with a microporous glass matseparator sandwiched between them, and wound in a jelly-roll manner.Thick inactive substrates used in such cell construction effectivelyreduce the energy density of the capacitor.

In yet another of its aspects, the present invention incorporates ultrathin film metal substrates in thin film electrochemical capacitors, inpreferred thickness less than 5 microns and more preferably less than 2microns. At present, minimum thickness available for some metallicelements, such as copper or aluminum foil, is about 5 microns. Bycontrast, conventional metal foils used for this purpose are typicallythicker. Typical metallic material is aluminum. However, copper, nickel,titanium, inconel, stainless steel, zinc, gold, valve metals, or anycompatible metallic elements or alloys with the overlying activeelectrode material will suffice. Preferably, when using valve metaloxides as the electrode material, the substrate is surface-enhanced andetched titanium foil. The most preferred thin designs of the new polymerelectrolytes of the present invention are preferably used together withvery thin electrode elements to provide thinner electrode/electrolytestructures (e.g., <<5 microns/<<5 microns) with very large surface areasand very thin inactive current collectors. These electrode/electrolytecombinations can be fabricated at low cost. A thin layer of activeelectrode material about 1 to 100 microns thick is applied or adhered tothe ultra thin metal substrate, as described below.

Alternatively, the electrode/electrolyte structures may use metallizedplastic or polymer substrate current collectors up to about 10 micronsthick, preferably 1-10 μm, instead of the above-described very thinmetallic element. The polymer substrate of each of the anode and cathodeis preferably selected from a group of polymers including polyester(PET), polypropylene (PP), polyethylene napthlate (PEN), polyethylene(PE), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyphenylenesulfide (PPS) and polytetrafluoroethylene (PTFE). Other polymermaterials that possess similar characteristics to these polymers couldalso be used and each polymer substrate is metallized to form theconductive layer thereon.

FIGS. 1A and 1B illustrate ultra-thin electrode structures employing aplain polymer substrate with a metal layer (sometimes referred to hereinas metallization layer) and an unmetallized margin. In FIG. 1A, an anode10 includes a plain polymer film substrate 12, e.g., polyester, with anoverlying metal layer 16 not entirely covering the substrate, to leavean unmetallized margin 14 of uncoated polyester. A thin coating ofactive anode material 20 is applied atop metal layer 16. In FIG. 1B,cathode 30 includes a plain polymer film substrate 40 which may beidentical to substrate 12 of the anode structure of FIG. 1A. Similarly,the polymer substrate 40 is metallized with a layer 50, except for anunmetallized margin 42. A layer of active cathode material 60 isdeposited or otherwise applied over metallization layer 50. As with theanode material 20 of the anode 10 of FIG. 1A, cathode material 60 doesnot extend onto the unmetallized margin. A thin layer of polymerelectrolyte 70 is then applied atop the cathode material 60, and likethe latter, does not extend into the margin 42.

Alternatively, the polymer substrate of the electrode structure may beimpregnated with an electronically conductive element that is inert tothe active electrode, and then metallized on both sides of the substratewithout a margin, as will be discussed in greater detail below inconjunction with a description of FIG. 3. Such an electronicallyconductive element may comprise conductive carbon, or an electronicallyconductive polymer such as polypyrrole, polyacetylene, or polyanilene,or other such material, or may be a finely ground and dispersed metalwhich is impregnated into the polymer substrate. The conductivity ofsuch an impregnated polymer substrate should be greater than 10² S/cm.These impregnated polymer substrates are particularly suitable forelectrode structures where the active electrode material is coated onboth sides of the metallized plastic current collector, or where bipolarhalf-elements are constructed.

Typically, the metallization material for the electrode structure isaluminum, but metals such as copper, nickel, titanium, inconel,stainless steel, zinc, gold, carbon, or any other metallization materialwhich is compatible with the overlying active electrode material issatisfactory. The selected thickness of the metallization layer dependsupon the particular conductivity requirement and the desired resistivityof the metal. Preferably, when using valve metal oxides as the electrodematerial, the metallization material is titanium. The polymer substratelayer may range in thickness, for example, from 0.5 micron to greaterthan 50 microns. Hence, the substrate is very flexible for ease ofcoating and handling, able to avoid kinking and deformation thereofduring manufacture of the electrochemical capacitors, and facilitatesthe production of a flexible electrode.

In an exemplary embodiment of an electrochemical capacitor, the activeelectrode material, such as RuO₂, is coated on a titanium metallizedpolymer. Each polymer substrate electrode material has different, easilyidentifiable, characteristics and thermal and mechanical properties, andeach behaves differently depending upon its use. A suitable material isreadily selected according to the desired properties. Ideally, the metalcoating should be as thin as possible, while concurrently having veryhigh conductivity. The coating thickness may have a conductivity of lessthan about 1.0 ohm per square, preferably less than 0.1 ohm per square,and more preferably about 0.01 ohm per square. This ensures lowresistance loss during current drain from the metallized substrate.

The metallization may be present on only one side of the polymer layeror substrate, but is preferably provided on both sides thereof Further,the metallization preferably is accomplished to leave an unmetallized(non-metallized) margin having a width in a range from about onemillimeter (mm) to about three mm. Where the metallization is present atboth sides of the polymer substrate, the non-metallization margin isprovided at opposite sides of the polymer material, but on the sameedge. When coated with the active material, the coating material isapplied to the metallized portion and not the margin. The use of suchsubstrates eliminates the use of additional carrier grids for theelectrodes and instead, the metallized plastic current collector canserve the purpose of both the carrier grid for the electrodes and thebattery enclosure—which provides a major cost benefit and reduces theinactive component and makes it lightweight, and further increases theenergy density of the capacitor.

The thin metal or metallized polymer substrate which as been describedherein is coated with very thin film active electrode material tocomplete an electrode structure that is thinner than known electrodesfor thin polymer electrolyte electrochemical devices. Conventionalcalendaring of the anode and cathode will not lead to the desiredthickness. Instead, the active electrode material is milled extensivelyin a solvent to reduce the particle size, and then injected directlyonto the substrate and subsequently drawn into thin films of any of avariety of predetermined thicknesses. Preferably the finely dividedelectrode material is blended with the polymer electrolyte solutionwhich is radiation curable. Furthermore, polymer electrolytes accordingto the present invention may also be manufactured using the sameprocess.

A number of different methods may be employed to cast or coat the activeelectrode material/polymer electrolyte composite from a solvent-basedsystem. Some suitable methods include knife coaters, doctor bladecoaters, screen-printing, wire-wound bar coaters or Mayer rods, airknife (or air doctor) coaters, squeeze roll or kiss coaters, gravurecoaters, reverse roll coaters, cast film coaters, and transfer rollcoaters. One coating system may be preferred over another to achieve aparticular intended final result. For instance, coaters that apply anexcess to the substrate web and remove the surplus coating, leaving adesired amount on the surface of the web are usually knife coaters,doctor blade coaters, bar or rod coaters, air knife coaters, and squeezeroll coaters. Coaters that apply a predetermined amount of coating tothe web include reverse roll coaters, gravure coaters, and transfer rollcoaters. Any of these methods may be suitable for coating dry polymerelectrolyte film thickness in the range of about 2 to 100 microns.

One preferred technique for applying an electrode/polymer electrolytecomposite material is to inject the electrode slurry with the finelydispersed inorganic and organic constituents directly onto thesubstrate, and then draw it out into a thin film of the desiredthickness using wire wound rods (Mayer rods) with different wirediameters. The different diameters of wire control the wet slurrythickness. This method, and the other electrode deposition techniquesdescribed herein have not been used previously in the electrochemicalcapacitor industry to manufacture electrodes. These methods greatlyfacilitate obtaining an electrode material/polymer electrolyte compositefilm that is extremely uniform, pin-hole free, flexible and ultra-thin.Film thickness of 2 microns to more than 100 microns can be controlledusing this process.

An alternative coating method includes incorporating each of the activeelectrode composites mixtures into its own aerosol mix and spraying anatomized aerosol of each material directly onto the respective oppositesides of the film substrate. This can be done rapidly while moving thesubstrate past the points of aerosol spray at high speed. The sprayedactive electrolyte materials are cured by drying, or by radiation if thematerial contains radiation curable polymeric materials. Anotheralternative method of coating the substrate with active electrodematerial is to evaporate the respective electrode materials directlyonto respective opposite sides of the substrate. In this case, it ispreferred that the polymer electrolyte blend include a liquid radiationcurable polymer capable of dissolving the metal salt and dispersing theinorganic materials. In such a case, liquid electrolyte solvents aremore suitable for use in dispersing the inorganic materials. Polymerelectrolytes and active electrode/polymer electrolyte compositesmanufactured in this manner can result in final film thickness of lessthan 1 micron and more preferably in thickness of about 0.2 micron orless.

One advantage of these thinner electrode structures is that they undergosignificantly less expansion and contraction during discharge and chargethan is typical with other electrode structures in an electrochemicalcapacitor with substantial redox reactions. The polymeric structureswithin the capacitor (i.e., the metallized film substrates, and polymerfilm electrolyte) should also accommodate these phenomena. Since thecomposite cathode and anode structures must be as thin and smooth aspossible and have a very high surface area, it is desirable to performextensive, high speed, wet attrition milling of the electrodeformulation. Final particle size of the composite electrodes is lessthan 0.1 micron, and preferably less than 0.05 micron. This will ensurea very thin film and smooth electrode during the coating process.

FIG. 2 illustrates a completed electrochemical capacitor using theelectrode structures of FIGS. 1A and 1B. Metal layers 102 a and 102 bare applied as terminations to opposite ends of the composite structurein which the anode 10 with substrate 12, metallization layer 16 andanode layer 20 is disposed atop the cathode 30, with anode layer 20directly overlying the polymer electrolyte layer 70. The arrangement issuch that the non-metallized margins 14 and 42 are positioned atopposite ends of the composite structure, so that when the metaltermination layers 102 a and 102 b are applied, they reside in directelectrical contact with the respective metallization/active electrodelayers 50/60 and 16/20.

As an alternative to the polymer substrate electrode structures of FIGS.1A and 1B, a dual electrode structure 25 for a thin film electrochemicalcapacitor is fabricated by laminating an electrode element on respectiveopposite sides of a double-metallized polymer substrate 13 to yield ahighly flexible and strong electrode structure for the capacitor, asillustrated in FIG. 1C. The double-metallized structure 25 comprisespolymer substrate 12 and metallization layers 16 a and 16 b on oppositesides (major surfaces) thereof with electrode elements 20 a and 20 blaminated (or otherwise applied) thereon, which leave non-metallizedmargins 14 a, 14 b provided on opposite sides of the polymer substrate.In a completed composite electrochemical capacitor structure using thedual electrode structures, the metal terminations are applied atopposite ends of the composite structure, similar to the manner oftermination shown in FIG. 2. Employing double-metallized substratesinstead of singly-metallized electrode substrates further increases theactive components of the capacitor and hence the energy density. It willbe readily understood that for metallic anode or cathode elements, thesurface resistivity will be significantly lower.

After the anode and cathode composite materials have been coated orlaminated onto either an ultra-thin metallic or a metallized plasticcurrent collector, as described above, the anode and cathode elementsare coated directly by a thin film polymer electrolyte.

Alternatively, the polymer substrate of an electrode may be impregnatedwith an electronically conductive element that is inert to the activeelectrode and metallized on both sides of the substrate without a margin(illustrated in FIG. 3). Such electronically conductive element couldinclude conductive carbon, electronically conducting polymers, e.g.,polypyrrole, polyacetylene, polyanilene, etc., or it could be finelyground, dispersed metal impregnated into the polymer substrate. Theconductivity of these impregnated polymer substrates should be greaterthan 10² S/cm. These designs of impregnated polymer substrates areparticularly useful when the active electrode material is coated on bothsides of the metallized plastic current collector or when bipolarhalf-elements are constructed. These impregnated polymer substrates areused in bipolar plates in a bipolar capacitor design and/or in monopolarcapacitor design. In both cases, however, the electrode terminations arenot end-sprayed at the electrode edges, as shown in FIG. 2, but insteadare end sprayed on the respective anode and cathode end units (notshown).

It is preferable that the monopolar capacitors not have the impregnatedpolymer substrates, so as to facilitate end-spraying for endterminations. However, the impregnated substrates are highly desirablefor bipolar designs. When impregnated substrates are used, nounmetallized margins are included. In addition, metallization of theimpregnated polymer substrate is optional. Typical metallizationmaterial is aluminum. However, copper, nickel, titanium, inconel,stainless steel, zinc, carbon, gold, or any compatible metallizationwith the overlying active electrode material will suffice. The chosenthickness of the metallic layer depends upon the particular conductivityrequirement and the desired resistivity of the metal.

A bipolar structure is fabricated by laminating anode and cathode activeelements on respective opposite sides of this conductive substrate.Preferably, the electrode layers are in a range of thickness from 0.1-50microns. For bipolar structures, the composite active cathode or anodeis preferably screen-printed onto the substrate element, but one of theabove-described techniques for applying active electrode composite maybe used instead.

The present invention thus provides very thin film, strong, and yetflexible and highly conductive polymeric electrolyte and electrodestructures, similar to film capacitor dielectric material that can betightly wound in formation of the capacitor.

Referring to FIG. 4, several webs are wound together in anelectrochemical capacitor structure. In particular, in this exemplaryembodiment three principal webs, comprising anode 310, hybrid polymerelectrolyte film 311 and cathode 312, are wound in the mannerillustrated in the Figure, or, alternatively, may be stacked orlaminated, to form electrochemical capacitor 315. A tightly woundconstruction removes air from between the layers, and allows enhancedand continuous contact between the layers. Care must be exercised toavoid electrical shorting of the beginning of the turns. The tightlywound capacitor is taped at the edge 326, and may then be strapped in atray (not shown) which is open on both sides. This provides access toboth ends 317 and 318 of the capacitor 315 for schooping or, preferably,metal spraying thereof, first with a high zinc content solder (hardermaterial) followed by a regular softer “Babbitt” end spray solder (90%tin: 10% zinc). The first end spray scratches the metallized surface andcreates a trough to build a better electrical and mechanical contact.The tight wind and offset spacing prevents the zinc from penetrating tothe active components. This combination of end sprays also allows bettercontact adhesion with the final terminations.

Subsequently, aluminum leads (not shown) are soldered onto each of theends 317 and 318 to form the final termination. The capacitor 315 maythen be epoxied to maintain pressure on the cell as well as to protectit further from humidity, and subsequently heated to about 80° C. for aperiod of from 2 to 5 minutes, to improve the interface. If desired, itmay be heated under vacuum before epoxying, to improve the interfaceeven further.

It will thus be recognized that polymer electrolytes fabricated in verythin film form can be used with thin film anode and cathode electrodes.By designing an electrochemical capacitor based on very thin film activeand inactive components, the surface area of the active plates can beeffectively increased to provide the capacitor with higher current draincapability, lower resistance, higher energy content, lower leakage, wideoperating temperature range, higher efficiency, higher capacityutilization, greater cycle life, and improved reliability and safety.Furthermore, when designed around very thin metallized polymer films (1micron) as the substrate material, the energy density may be expected toimprove by at least 25 to 40% over state-of-the-art electrochemicalcapacitors, with reduced cost. A method of producing cells with theabove attributes is to manufacture very thin film cell components, andonce the individual cell components have been laminated, the finishedcell is heated to about 60-80° C. for about 2 hours. This enhances theelectrode/electrolyte interface and allows better interfacial adhesionand improved cyclability.

Although certain preferred embodiments and methods have been disclosedherein, it will be appreciated by those skilled in the art to which theinvention pertains, from a consideration of the foregoing description,that variations and modifications may be made without departing from thespirit and scope of the invention. Accordingly, it is intended that theinvention shall be limited only by the appended claims and the rules andprinciples of applicable law.

What is claimed is:
 1. An electrochemical capacitor, comprising anionically conductive polymer thin film, liquid electrolyte retained insaid thin film, and thin flexible active electrode layers constitutingan anode and a cathode composed of energy dense material of highintrinsic surface area positioned at either side of said thin film totightly sandwich said electrolyte-retaining thin film therebetween. 2.The electrochemical capacitor of claim 1, wherein said electrode layershave a thickness in a range from about 1 micron to about 100 microns. 3.The electrochemical capacitor of claim 1, wherein said electrode layerscomprise an electrode active material blended with a polymerelectrolyte.
 4. An electrochemical capacitor, comprising an ionicallyconductive polymer thin film, a liquid electrolyte retained in said thinfilm, and thin flexible active electrolyte layers constituting an anodeand a cathode composed or energy dense material of high intrinsicsurface area positioned at either side of said thin film to tightlysandwich said electrolyte-retaining thin film therebetween, wherein saidenergy dense material consists of at least one first group materialpossessing properties of high exchange current density, intrinsicallyhigh surface area, and high charge capacity in combination with at leastone second group material essentially having exceptionally high redoxcapacity.
 5. The electrochemical capacitor of claim 4, wherein saidenergy dense material has a composition comprising about 1% to 99% byweight of said energy dense material of said first group material andthe remainder of said energy dense material comprising said second groupmaterial.
 6. The electrochemical capacitor of claim 4, wherein saidfirst group material is based on activated carbon.
 7. Theelectrochemical capacitor of claim 4, wherein said first group materialcomprises valve metal oxide selected from the group consisting of oxidesof titanium, zirconium, hafnium, niobium, tantalum, molybdenum,tungsten, ruthenium, iridium, platinum, palladium, osmium, gold, andrhenium.
 8. The electrochemical capacitor of claim 7, wherein saidsecond group material comprises battery active material selected fromthe group consisting of oxides, sulfides and selenides, including any ofMnO₂, LiMn₂O₄, Li_(x)MnO₂, MoS₂, MoS₃, MoV₂O₈, CoO₂, Li_(x)CoO₂, V₆O₁₃,V₂O₅, V₃O₈, VO₂, V₂S₅, TiS₂, NbSe₃, Cr₂O₅, Cr₃O₈, WO₃, Li_(x)NiO₂,Li_(x)N_(y)Co_(z)O₂, Li_(x)Ni_(y)Mn_(z)O₂, Li_(x)Co_(y)Mn_(z)O₂, andlithium doped electronically conducting polymers including polypyrrole,polyaniline, and polyacetylene.
 9. The electrochemical capacitor ofclaim 4, wherein said first group material is physically mixed with saidsecond group material as said energy dense material in said electrodelayers to enhance the discharge time of said capacitor.
 10. A thin filmelectrochemical capacitor, comprising a resilient flexible ionicallyconductive polymeric thin film including a base polymer with inorganicfiller dispersed therein to increase surface area and porosity of saidpolymeric thin film; a liquid electrolyte composed of liquid polymer,organic solvent electrolyte and a salt in solution impregnated in saidpolymeric thin film to form a gelled thin film polymer electrolyte; anda pair of spaced-apart flexible thin film electrodes, each of saidelectrodes adhered to a current collector thereon, wherein saidpolymeric thin film is tightly sandwiched between said pair of thin filmelectrodes.
 11. The thin film electrochemical capacitor of claim 10,wherein said polymer electrolyte is a cation conductor.
 12. The thinfilm electrochemical capacitor of claim 10, wherein said polymerelectrolyte is dimensionally stable and of high mechanical strength. 13.The thin film electrochemical capacitor of claim 10, wherein saidpolymer electrolyte is temperature stable up to 120° C.
 14. The thinfilm electrochemical capacitor of claim 10, wherein said polymerelectrolyte is in the form of a very thin film.
 15. The thin filmelectrochemical capacitor of claim 10, wherein said polymer electrolytehas low resistance and high flexibility.
 16. The thin filmelectrochemical capacitor of claim 10, wherein each said currentcollector is a very thin structure chosen from the group consisting ofmetallic elements 1 to 10 μm thick and metallized plastics 0.5 to 50 μmthick.
 17. The thin film electrochemical capacitor of claim 10, whereineach said current collector is a metallic current collector selectedfrom the group consisting of aluminum, nickel, copper, titanium,stainless steel, and an alloy including inconel.
 18. The thin filmelectrochemical capacitor of claim 10, wherein said base polymer has apredominantly amorphous structure.
 19. A thin film electrochemicalcapacitor, comprising a resilient flexible ionically conductivepolymeric electrolyte thin film including a base polymer with inorganicfiller dispersed therein to increase surface area and porosity of saidpolymeric thin film; a liquid electrolyte composed of liquid polymer,organic solvent electrolyte and a salt in solution impregnated in saidpolymeric thin film; and a pair of spaced-apart flexible thin filmelectrodes, each of said electrodes adhered to a current collectorthereon, wherein said polymeric electrolyte thin film is tightlysandwiched between said pair of thin film electrodes, wherein each saidcurrent collector is a metallized polymer current collector comprising apolymer substrate about 0.5-50 μm thick and a metallization layer up to1 μm thick overlying at least a portion of said polymer substrate. 20.The thin film electrochemical capacitor of claim 19, wherein saidpolymer substrate of each of said thin film electrodes is selected froma group of polymers including PET, PP, PPS, PEN, PVDF and PE, saidmetallization layer on each said polymer substrate forming anelectrically conductive layer thereon.
 21. The thin film electrochemicalcapacitor of claim 20, wherein each metallized polymer substrate has athickness in a range from about 0.5 micron to about 50 microns.
 22. Thethin film electrochemical capacitor of claim 20, wherein each saidmetallization layer is selected from a group consisting of aluminum,copper, nickel, titanium, inconel, stainless steel, zinc, gold, andcarbon.
 23. The thin film electrochemical capacitor of claim 20, whereineach said electrode is a valve metal oxide.
 24. The thin filmelectrochemical capacitor of claim 23, wherein each said metallizationlayer is titanium.
 25. The thin film electrochemical capacitor of claim24, wherein each said valve metal oxide is RuO₂.
 26. A thin filmelectrochemical capacitor, comprising a resilient flexible ionicallyconductive polymeric electrolyte thin film including a base polymer withinorganic filler dispersed therein to increase surface area and porosityof said polymeric thin film; a liquid electrolyte composed of liquidpolymer, organic solvent electrolyte and a salt in solution impregnatedin said polymeric thin film; and a pair of spaced-apart flexible thinfilm electrodes, each of said electrodes adhered to a current collectorthereon, wherein said polymeric electrolyte thin film is tightlysandwiched between said pair of thin film electrodes, wherein each ofsaid thin film electrodes comprises a layer of polymer material, and alow resistance metallization layer having a conductivity in a range fromabout 0.01 ohm per square to about 1 ohm per square overlying andadhered to a side of said layer of polymer material.
 27. The thin filmelectrochemical capacitor of claim 26, wherein each of said thin filmelectrodes has a thickness in a range from about 0.5 micron to about 50microns.
 28. The thin film electrochemical capacitor of claim 26,wherein each said layer of polymer material has a non-metallized marginwith a width in a range from about one mm to about three mm.
 29. Thethin film electrochemical capacitor of claim 28, wherein each said layerof polymer material has a low resistance metallization layer of saidconductivity adhered to each side thereof, and both sides of said layerof polymer material have a non-metallized margin with said width at thesame edge of said layer of polymer material.
 30. The thin filmelectrochemical capacitor of claim 29, wherein active electrode materialis applied over said low resistance metallization layer on each saidlayer of polymer material and not on said non-metallized margin of saidlayer of polymer material.
 31. The thin film electrochemical capacitorof claim 30, wherein said active electrode material comprises RuO₂.